The filmmaker watched plenty of movies to research his project, but nothing could have prepared him for encountering animal death up close.

In “Okja,” Korean director Bong Joon Ho takes the excitement of a family-friendly sci-fi adventure and turns it into a nightmarish look at the fast food industry. The movie, which premiered in competition last month at the Cannes Film Festival, surrounds the efforts of a multi-national company to mass-produce mutant pigs for slaughter. When one of them bonds with a young girl in the mountainside, she risks her life to save the titular being from decimation — a fast, fun journey that culminates in a horrific sequence set in the confines of a slaughterhouse.

While the shocking imagery involves the death of imaginary animals, it has clear parallels with the grotesque images of vivisected cows and other livestock that meet grisly ends in real meathouses around the world. To prepare for the sequence, Bong and producer Dooho Choi visited a slaughterhouse in Colorado — and the experience turned both of them into temporary vegans.

“It was a very overwhelming experience,” Bong said during a Q&A following a guild screening of the film at the Museum of Art and Design. “When I returned from Colorado to New York [where some of ‘Okja’ was shot], I felt like the smell was following me there.”

That became the foundation for his discussion about how to write the scene.“Bong decided that it would be a disservice [to the movie] if the slaughterhouse weren’t disturbing,” his co-screenwriter, Jon Ronson, added.

“Okja”

Cannes Film Festival

Prior to the trip, Bong watched a series of documentaries set in slaughterhouses to familiarize himself with the imagery. These included “La Parka” (“The Reaper”), Nicaraguan director Sergio Arguello’s 2015 Oscar-nominated short film about a man who has spent 25 years killing bulls. He also watched the 2005 feature “Our Daily Bread,” from Austria’s Nikolaus Geyrhalter, a collage of food processing plans depicted in graphic details. But even those movies couldn’t prepare the director for the visceral experience he encountered in Colorado.

“When you’re finally there, there’s this smell. There is no smell in the films,” he said. For the next two months, he remained vegan. “Then I flew back to South Korea, and you know, Korea is a BBQ paradise,” he said with a laugh. “Every street on every corner is burning meat. I slowly, slowly came back to being a meat eater.”

Still, the experience continues to have an effect on him. “In the process of making this movie, my level of meat consumption has decreased,” he said. “Now I’m gradually becoming a pescatarian.” The announcement was met with applause by the appreciative crowd.

“Okja” comes out on Netflix and in select theaters worldwide on June 28.